Note: Descriptions are shown in the official language in which they were submitted.
VEHICLE SUSPENSION MEMBER AND METHOD FOR MAKING
INTRODUCTION
This invention relates generally to a vehicle sn~rrn~ion member and
method for making same ~yrmp1qry of which is a leaf spring col,lplising a
singular or plurality of leafs or plates of which at least one has at least one
S ~ . on~ ui1y therewithin that is s11hstqntiq11y parallel to the loneitl-~inql axis
t-YtPn-line between opposite ends thereof and effective of redirect or divert crack
p~up~dlion in a direction generally parallel thereto.
BACKGROUND OF THE INVENTION
Although coil springs have recently come into favor for p~cif.1ge1 car
s~pen~ion systems, leaf springs remain in favor for use particularly in truck
~u~pe~ on systems and are likely to for many years to come because of the load
capacity, p7rkaPine and axle location advantages acs~i~1Pd therewith. Although
desc~ d herein with particularity to leaf springs, the present invention includes
any vehicle s ~ Oll member subject to torsional or bending loads and having a
long;~"l;n~l axis e~t~ l;ng between opposite ends such as torque rods (also called
trailing arms) for axle control; traction bars (keep axle from twisting during
braking); and track rods (keep axle from shifting laterally).
Leaf springs generally co~ 1iae a singular leaf or plate or a plurality of
leafs or plates of s~,l,a~ 11y constant or tapered thirl~n~c most commonly made
from steel and secured together and operative to support the frame of the vehicle
on the wheel axle. As might be t-l~'~l the number of leafs or plates e.11~loy~d
in the leaf spring is based on allowable design stress for a given load capacity and
cleflPction range.
Each plate or a leaf spring is subjected to cantilever bending p1uJucillg a
(positive) tensile stress on the upper, typically concave, surface of the leaf to
which the vehicle load or force is applied. As a result, a bq1qnrine (negative)
con1~ ai~/e stress is developed on the lower, typically convex, surface of the
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7~3~
leaf. The tensile stress is a maximum at the upper surface of the leaf and
decreases to zero at or near the center of the plate thi~L n~ also known as the
neutral axis hereinafter referred to as the longituclin~l axis extending betweenopposite ends of the plate or leaf. Similarly, the b~l~ncing co.u~ /e stress is
a m~l~imllm on the lower surface d~ ining to zero at the lon~it~ in~l axis.
Virtually all cracks are initiated at or near the upper surface of the leaf spring
plate at the point of m~timllrn tensile stress.
Due to high strength ~C4Uilt;llle.llS, leaf springs must have high hd,~llluss
which causes them to be prone to rapid crack propagation through the leaf cross-section once a relatively shallow crack is developed at the tensile surface. Theinrid~nr,e of crack initi~tion and ~c,gr~;on is generally a function of inc-cased
service life or time and also service conditions inrllltling load history and
cullu~ion. No matter how a crack may develop, i.e., fatigue and/or corrosion,
its l~lugl~ s~;on beyond a critical depth of generally less than one-half of section
îl"~'L~ iS rapid to complete fracture or se~r~tion. The present invention
initiates at or near the upper tensile surface and ~lobl~esses through the tl~ L~f CC
of the leaf or plate in a direction generally perpen~lic~ r to the lon~ilu~ l axis
of the leaf by ~cdil~ling crack p~ùbl~s~ion to a direction generally parallel
theretû. Effectively, the parallel crack or d~ in~ion of the flat (or tapered)
plate section lowers section stiffness causing the spring to sag well before final
fracture providing the user some early inr1ir~ti--n of ;~ g spring failure priorto c .' s~ l;on and possible vehicle debilitation.
SUMMARY OF THE INVENTION
Accordi.lgly, it is an object of this invention to provide a vehicular
s~ member such as a leaf spring comprised of at least one plate that is
adapted to divert or redirect crack prop~"~tion in a direction generally parallel to
a longitn~lin~l axis e~ between opposite ends thereof.
BRlEF DESCRlPI ION OF THE DRAWlNGS
FIGURE 1 is a side view of a vehicle s~ on leaf spring 50 showing
the Icdir~iled crack propag~ion;
3 ~
FIGURE 2 is a sche,.,~ic block diagram of a method of nnaking a leaf or
plate 22 from a billet 10 having a central void or from a tubular section 14;
FIGURE 3 is a sche~l,A~ic block diagram of a method of making a plate or
leaf from a billet having a plurality of voids or cavities 28;
FIGURE 4 is a SCI~e~AI;C block diagram of a method of making a leaf or
plate 32 from a folded member 34; and
FIGURE S is a acl~e ll ~ block diagram of a method of making a leaf or
plate 42 from a yl~ ru~ ed billet member 41 having opposite inwardly concave
sidewalls.
DESCRIPIION OF SOME PREFERRED EMBODIMENTS
Leaf spring 50 in FIGURE 1 co-~ ises singular leaf or plate 2 that
extends between opposite ends thereof (not shown) that are adapted such as by
being formed into eyelets to secure plate 2 to a vehicle frame. Commonly, only
one plate is a stacked plurality of spring leaf plates need have eyelets at one or
both its opposite ends. In some ~ s it may be preferable to omit eyelets.
Althûugh shown in FIGURE~ 1 as tapering in a di-~;lion towards it opposite ends
to provide the thickest section at its center, plate 2 may also have a s~lJa~ y
constant ll.;-'L..~ lhl~ughoul its entire length as previously d~s~ ed and well
known to those skilled in leaf spring art.
As earlier ~l~sc~ d plate 2 may be just one of a plurality of stacked leafs
or plates that are secured together to provide the S~J~IX ~ n system for a vehicle.
Plate 2 is co.... o~ly made from a suitable spring steel alloy and has a
substantially rectangular cross s~:lion and a longitudinql axis "L/A" l~ f~.~ nced by
numeral 4 that extends therealong between its opposite ends.
For illustrative yu"~SCS, l~ bending loads "P" and "P~" have been
r~ Iy applied to opposite ends of plate 2 at the point of s~ul~ e.ll (not
shown) that have created reaction force "F" at the spring seat (co---lllonly
bridging the center) which has l~l~in~qt~ly caused a crack to occur at the uppertensile surface due to fatigue as denoted by lerel~ nce numeral 8. But rather than
crack completely through plate 2 in a direction generally transverse to axis
"L/A", the crack pl~p~g~ ~;on has been directed or diverted for a distance "L" in
3 2
a direction generally parallel to axis "L/A" and Illtim~tely exits on the bottomside as referenced by numeral 8' because of a discontinu,ty that was purposely
introduced within plate 2 as hel~indrlcr descnhed.
As usecl herein, the word "rli~co"~ y" means a rli~. o~ ..ll;Ly in
S mec~h~nir ~l properties situated along a single plane or along multiple planes that
are disposed in a direction generally parallel to the lon~itllrlin~l axis but not
neces~dlily continuous therealong. In inct~nres where the s~c~ c;ol member is a
leaf or plate subject to bending loads, the ~ CQ.~ y iS p~cÇ~ly disposed near
the neutral iaxis of the leaf or plate.
One method by which to h~Llwlllce a ~ colll;.. uily within the leaf or plateis shown in FIGURE 2 where the starting ~IIU-;IU1C~ iS either a billet 10 made
from a selected spring steel alloy having a void 12 r~ ler~ g along a central
region thereof or a metal tubular section 14 having a void or opening 16
eYtending centrally the.tll,rvu~,l,. When mave from steel, billet 10 is preferably
heated in step (b) to a pl~elc.,l~ined ~r-~ ~ such as from about 1700~F to
about 2200~F and then cvll,~ J~ed in step (c) between rollers 18 and 18' or by
other suitable cs , ~ ;on means into plate 20 so as to col.l~,.ess surfaces
surrounding void 12 or void 16 together in a manner effective to form
~Ji~o~ y 22 that is generally parallel to and in ~Jl~s~ nm-o.n~ with a~cis
"L/A" and err~ili~ to divert or redirect crack plUp~ in a ~ ~;lion
generally parallel thereto. After co"l~)rt,i,i,;on, plate 20 is cooled to ambient
te..l~alu~e in step (d) in i~ 5 where it is heated in step (b).
In FIGURE 3, a member such as billet 26 made from a selected spring
steel metal is provided with plurality of voids 26 therein step (a). As previously
~le";~ ;hed when made from steel, the member is preferably heated to a
p.cdct~lllined t~ -U~-e such as from about 1700~F to about 2200~F in step ~b)
and co..l~ sed in step (c) into plate 30 between rollers 18 and 18' or other
suitable cGI~.p~.on means so as to COIl~ 5 surfaces ~ull.)unding voids 28
together in a manner effective to form respective ~i~rQn~ ;es 32 th~ t~n
that are generally parallel to each other and to iaxis "L/A" afterwhich plate 30 is
cooled to ambient l..l~ lure in step (d) in jnct~n~es where it is heated in step
~7~ ~2
(b). Discontinuities 32 are effective to divert the crack in a direction generally
parallel to axis "L/A".
Another method of making vehicle suspension ~l~el~bel~ in accordance
with the invention is shown in FIGURE 4 where a flat member 34 made from a
selected spring steel metal alloy is provided in step (a) and, when made from
steel, is preferably heated to a ~)redelel.l.,ned te---~;ldlure of about 1700DF to
about 220~'F in step (b) and folded in step (c) such that it has a generally U
shaped cross-se~ti--n~l configuration having a closed end 35 and an open end 37
after which it is co-~ ;,s~ in step (d) between rollers 18 and 18' or other
suitable co.. plc~,Oion means to provide plate 36 with the facing surfaces on
opposite sides of the U shaped opening being co.--~)ressed together in a manner
effective to form ~liccof~ u;ly 38 therebetween that is generally parallel to axis
"L/A" and effective to divert or redirect crack plop~e~lion in a direction
generally parallel thereto. Plate 36 is cooled to ambient le..l~ldlule in step (e),
in inC~ ces where it is heated in step (b).
Yet another method of making a leaf or plate for a vehicle su~n~icln
system in accord~ce with the invention is shown in FIGURE S in which a billet
41 or the like is provided in step (a) having opposite sidewalls (43,43') that in
cross sf~ion have an inwardly concave conrlguldlion created by either casting orby previous rolling history. When made ~rom metal, billet 41 of step (a) is
preferably heated to a p,~ete.,l,incd le.ll~.dlulG in step ~b) and then co",l"~ OS~ d
into plate 42 in step (c) between rollas 18 and 18' or other suitable COIlllJlei~oiOn
means so that the side wall surfaces defining the inwardly concave confi~,wdlions
are COI~ oo~ together in step (c) in a manner effective to form respective
.l;~ s 44 and 41' eYten~ing along opposite sides thereof that are
generally parallel to axis "L/A" and effective to deter crack plu~ ion in a
direction generally parallel to axis "L/A" and effective to deter crack plup~O';on
in a di,~ion generally parallel thereto.
Plate 42 is cooled to ambient L~ tllre in step (d) in i~ ces where it
is heated in step (b).
Although shown solely as voids such as voids 12 or 16 in FIGURE 2 and
voids 28 in FIGURE 3 and opening 37 in FIGURE 4 and inwardly concave edges
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~7~32
43 and 45' in FIGURE 5, it is to be understood that such voids may contain
such as metal or ceramic fibers to impart the member with desired
s.,~ on ch~-art~ristics-
Thus, the invention provides vehicle s~pçn~ion members such as leaf
S springs that are operative to signal impending failure by providing at least one
continnity therein that is effective to divert or direct crack propagation in a
direction generally parallel to longit~ in~l axis "L/A" eYtPnrling therealong
between opposite ends of the leaf or plate.
